"I think when he calls me 'brilliant', I'll take the compliment, OK?" said the businessman, adding that Mr Putin had "great control over his country".

Mr Trump also said that, as a result of the confidential intelligence briefings he has been entitled to as an election candidate, he had been "shocked" at how the president, Mrs Clinton and current Secretary of State John Kerry had done "exactly the opposite" of what intelligence experts had told them.

In the forum, Mr Trump also said: "I was totally against the war in Iraq."

This appeared to contradict a statement in a 2002 interview with radio host Howard Stern and the forum's moderator, Matt Lauer, came in for intense criticism after the event for not pressing Mr Trump on the statement.

Mr Obama said in Laos: "The most important thing for the public and the press is to just listen to what he says and follow up and ask questions to what appear to be either contradictory or uninformed or outright wacky ideas".

Mrs Clinton had found herself once again on the defensive during the forum over her private email server.

The forum offered a preview of the questions they will face in their three forthcoming presidential debates, the first at Hofstra University near New York on 26 September.